This invention relates to a throttling valve for controlling the flow of liquids to produce quiet flow conditions at relatively high flow rates.
Valve noise has become of increasing concern lately for reasons of environmental safety. Numerous valve configurations have been developed over the last thirty years in attempts to either suppress or control noise. In many of the earlier devices, the valve and its surrounding flow channels are wrapped with acoustical materials for absorbing sound. Later designs involve fixed and movable attenuators which are placed directly into the flow path to divide the main flow stream into a series of subflows or to shape the geometry of the flow. Attenuators, however, represent obstructions in the flow path which create special design considerations and which can, under certain operating conditions, produce rather than suppress noise.
Flow interrupting devices have also been proposed in the prior art which act on the moving fluid to shift the noise frequency out of the audible range. One such device is described in U.S. Pat. No. 4,150,696 to Meier et al. Here again, the frequency shifting mechanism typically obstructs flow and thus can disrupt the normal flow pattern of the fluid as it moves through the valve.
The prior art has generally been concerned with suppressing existing valve noise once it has been generated. The present invention is concerned with eliminating or avoiding factors that create noise producing vibrations. These factors may be either flow related or mechanical in nature. These noise producing factors may include such things as cavitation, turbulent flow conditions, fluid separation at the flow boundaries, and obstructions in the flow path.